Ligand exchange reactions of Re2(u-OR)3(CO)6r (R = H, Me) with sulfur, selenium, phosphorus and nitrogen donor ligands, investigated by electrospray mass spectrometry

Article abstract of DOI:10.1039/b003897k

Negative-ion electrospray mass spectrometry has been used to investigate the reactions of the dinuclear rhenium aggregates [Re2(u-OH)3(CO)6]- 1 and [Re2(u-OMe)3(CO)6]- 2 with a range of thiols, benzeneselenol, and some other sulfur-, phosphorus- and nitrogen-based ligands. Typically up to three of the hydroxo ligands are replaced by simple thiolates, giving the series of species [Re2(OH)2(SR)(CO)6]-, [Re2(OH)(SR)2(CO)6]-, and [Re2(SR)3(CO)J-. Similarly, reaction of 1 with H2S gives the species [Re2(u-SH)3(CO)6]-, which undergoes an analogous fragmentation process to [Re2(u-OH)3(CO)6r, at high cone voltages, by loss of H2S and formation of [Re2(S)(SH)(CO)6]-. With ligands which are good chelating agents (such as dithiocarbamates R2NCS2-, and thiosalicylic acid, HSC6H4CO2H) initial substitution of one or two OH groups readily occurs, but on standing the dimer is cleaved giving [Re(S2CNR2)2-(CO)3]- and [Re(SC6H4CO2)(CO)3]-. The different reactivities of the dithiol reagents benzene-1,2- and benzene-1,4-dimethanethiol towards 1 are also described. Complex 1 also reacts with aniline, and with primary (but not secondary) amides RC(O)NH2, giving monosubstituted species [Re2(OH)2(NHPh)(CO)6]- and [Re2(OH)2{NHC(O)R}-(CO)6]- respectively. The reactions with adenine and thymine, and with the inorganic anions thiocyanate and thiosulfate, are also described. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b003897k

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Ϫ
Ligand exchange reactions of [Re (ꢀ-OR) (CO) ] (R ؍ H, Me)
2
3
6
with sulfur, selenium, phosphorus and nitrogen donor ligands,
investigated by electrospray mass spectrometry†
a
a
b
c
Chenghua Jiang, T. S. Andy Hor,* Yaw Kai Yan,* William Henderson* and
c
Louise J. McCaffrey
a
Department of Chemistry, Faculty of Science, 3 Science Drive 3, National University of
Singapore, Kent Ridge 119260, Singapore
Division of Chemistry, National Institute of Education, Nanyang Technological University,
b
4
69 Bukit Timah Road, Singapore 259756
c
Department of Chemistry, University of Waikato, Private Bag 3105, Hamilton, New Zealand
Received 16th May 2000, Accepted 27th July 2000
Published on the Web 30th August 2000
Negative-ion electrospray mass spectrometry has been used to investigate the reactions of the dinuclear rhenium
Ϫ
Ϫ
aggregates [Re (µ-OH) (CO) ] 1 and [Re (µ-OMe) (CO) ] 2 with a range of thiols, benzeneselenol, and some other
2
3
6
2
3
6
sulfur-, phosphorus- and nitrogen-based ligands. Typically up to three of the hydroxo ligands are replaced by simple
Ϫ
Ϫ
Ϫ
thiolates, giving the series of species [Re (OH) (SR)(CO) ] , [Re (OH)(SR) (CO) ] , and [Re (SR) (CO) ] . Similarly,
2
2
6
2
2
6
2
3
6
Ϫ
reaction of 1 with H S gives the species [Re (µ-SH) (CO) ] , which undergoes an analogous fragmentation process
2
2
3
6
Ϫ
Ϫ
to [Re (µ-OH) (CO) ] , at high cone voltages, by loss of H S and formation of [Re (S)(SH)(CO) ] . With ligands
2
3
6
2
2
6
Ϫ
which are good chelating agents (such as dithiocarbamates R NCS2 , and thiosalicylic acid, HSC H CO H) initial
2
6
4
2
substitution of one or two OH groups readily occurs, but on standing the dimer is cleaved giving [Re(S CNR ) -
2
2 2
Ϫ
Ϫ
(
CO) ] and [Re(SC H CO )(CO) ] . The different reactivities of the dithiol reagents benzene-1,2- and benzene-
3 6 4 2 3
1
,4-dimethanethiol towards 1 are also described. Complex 1 also reacts with aniline, and with primary (but not
Ϫ
secondary)amidesRC(O)NH , givingmonosubstitutedspecies[Re (OH) (NHPh)(CO) ] and[Re (OH) {NHC(O)R}-
2
2
2
6
2
2
Ϫ
(
CO) ] respectively. The reactions with adenine and thymine, and with the inorganic anions thiocyanate and
6
thiosulfate, are also described.
Introduction
phosphine ligand) and H S, thiols and primary or secondary
2
2
phosphines. However, the Re(CO)3 unit also forms stable
1
In the preceding paper we described the use of negative-ion
electrospray mass spectrometry (ESMS) for analysis of the
3,4
complexes with hard ligands such as hydroxide, indicating
that it does not fit comfortably into the ‘traditional’ hard–soft
acid–base scheme.
rhenium carbonyl hydroxo(alkoxo) complexes [Re (µ-OH) -
2
3
Ϫ
Ϫ
(
CO)6] 1 and [Re (µ-OMe) (CO) ] 2, including the various
2 3 6
Results and discussion
General comments
The analysis of the dinuclear rhenium carbonyl hydroxo com-
plex 1 by negative-ion electrospray mass spectrometry is
1
described in the preceding paper. Spectra at low cone voltages
Ϫ
(
5–20 V) are dominated by the parent ion [Re (µ-OH) (CO) ]
2 3 6
at m/z 591, so that exchange reactions with various ligands can
easily be monitored by simply adding a small quantity of the
ligand to a solution of 1, and then recording the ESMS
spectrum at different times.
fragmentation pathways observed for these species and their
exchange reactions with other oxygen donor ligands. In this
paper we describe the ligand exchange reactions of 1 with vari-
ous sulfur-, selenium-, phosphorus- and nitrogen-based ligands.
Complex 1 contains rhenium() and is therefore expected to
have a strong affinity for soft donor ligands. Indeed, reactions
of rhenium alkoxo complexes with second-row substrates such
as thiols and secondary phosphines are considered to be
irreversible, such as between the monorhenium complexes
The ligands investigated include a series of mono- and di-
thiols, benzeneselenol, thiocyanate, dithiocarbamates (R N-
2
Ϫ
CS2 ), together with some difunctional thiol-based ligands
such as thiosalicylic acid (HSC H CO H) and 3-sulfanyl-
6
4
2
propionic acid, HSCH CH CO H. The primary phosphine
2
2
2
5
5
[
Fe(η -C H )(η -C H CH PH )] was also studied for compar-
5 5 5 4 2 2
ative purposes. The reactions of amines and amides have also
been investigated.
[
Re(OR)(CO) L ] (R = Me or Et, L = bidentate arsine or
3
2
2
Full details of the m/z values and relative intensities of the
various major ions observed in this work are summarised in
the electronic supplementary data. In all cases, the unchanged
†
Probing the chemistry of the dinuclear rhenium carbonyl complexes
Ϫ
2 3 6
[
Re (µ-OR) (CO) ] (R = H or Me) by electrospray mass spectrometry.
Part 2.
Ϫ
Ϫ
[
Re (µ-OH) (CO) ] and [Re (OH) (CO) ] ions were typically
2 3 6 3 4 9
Electronic supplementary information (ESI) available: full ES data
for the reactions of complexes 1 and 2 with S- and Se-based ligands.
See http://www.rsc.org/suppdata/dt/b0/b003897k/
observed, particularly in the early stages of the reaction. At
higher cone voltages (30–50 V) the dehydrated ion [Re (O)-
2
3
204
J. Chem. Soc., Dalton Trans., 2000, 3204–3211
This journal is © The Royal Society of Chemistry 2000
DOI: 10.1039/b003897k

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a
Ϫ
Table 1 Major negative ions observed in reactions of the complexes [Re (µ-OH) (CO) ] 1 with p-toluenethiol, thiosalicylic acid and H S in MeCN
2
3
6
2
Cone voltage/V
(reaction time)
Mixture
Ions (m/z)
[Re (OH) (CO) ] (591), [Re (OH) (SR)(CO) ] (697), [Re (OH) (CO) ] (879, trace)
؊
Ϫ
Ϫ
1
ϩ p-MeC H SH
5 (20 min)
6
4
2
3
6
2
2
6
3
4
9
؊
Ϫ
Ϫ
5
(overnight)
[Re (OH) (SR)(CO) ] (697), [Re (OH)(SR) (CO) ] (803), [Re (OH) (CO) ] (879,
2 2 6 2 2 6 3 4 9
Ϫ
trace), [Re (SR) (CO) ] (909, trace)
2
3
6
؊
Ϫ
Ϫ
5
(1 week)
[Re (OH)(SR) (CO) ] (803), [Re (OH) (CO) ] (879, trace), [Re (SR) (CO) ] (909)
2
2
6
3
4
9
2
3
6
Ϫ
؊
؊
1
ϩ thiosalicylic acid (H tsal)
5 (1 min)
[Re (OH) (CO) ] (591, trace), [Re (OH)(tsal)(CO) ] (709), [Re (OH) (Htsal)(CO) ]
2 3 6 2 6 2 2 6
Ϫ Ϫ
2
(
727), [Re (OH)(tsal)(MeCN)(CO) ] (750), [Re (OH) (CO) ] (879)
2 6 3 4 9
Ϫ ؊
5
5
(10 min)
[Re (OH) (CO) ]
(591, trace), [Re (OH)(tsal)(CO) ]
(709), [Re (OH) (Htsal)-
2 2
Ϫ
2
3
6
2
6
Ϫ
Ϫ
(
CO)6] (727), [Re (OH)(tsal)(MeCN)(CO) ] (750), [Re (OH) (CO) ] (879)
2 6 3 4 9
؊ Ϫ
(overnight)
[Re(tsal)(CO)3] (423), [Re(tsal)(CO) (NH )] (440)
3 3
؊ Ϫ
Ϫ
1
ϩ H2S
5 (35 min)
[Re (OH) (CO) ] (591), [Re (OH) (SH)(CO) ] (607), [Re (OH)(SH) (CO) ] (623),
2 3 6 2 2 6 2 2 6
Ϫ
[
Re (SH) (CO) ] (639)
2 3 6
؊
Ϫ
Ϫ
5
5
(overnight)
[Re (SH) (CO) ] (639) plus traces of [Re (OH) (CO) ] (591), [Re (OH) (SH)(CO) ]
2 3 6 2 3 6 2 2 6
Ϫ
(
607), [Re (OH)(SH) (CO) ] (623)
2 2 6
Ϫ
Ϫ
؊
0 (overnight)
[Re (S)(SH)(CO) ] (549), [Re (S)(SH)(CO) ] (577), [Re (S)(SH)(CO) ] (605),
2 4 2 5 2 6
Ϫ
[
Re (SH) (CO) ] (639)
2 3 6
a
32
The m/z value refers to the peak of greatest intensity in the isotope distribution pattern, calculated using the ISOTOPE program. The major ions
observed are indicated in bold type.
Ϫ
(
OH)(CO)6] was also seen. These ions will not further be
commented upon in the discussion.
Reactions of complexes 1 and 2 with monofunctional thiols and
PhSeH
Addition of p-toluenethiol (RSH) in excess to complex 1 results
Ϫ
initially in a mixture of the species [Re (OH) (SR)3 Ϫ n(CO)6]
2
n
(
n = 0–3) which on standing overnight gives mainly the mono-
Ϫ
and bis-thiolate anions [Re (OH) (SR)(CO) ] (m/z 697) and
2
2
6
Ϫ
[
Re (OH)(SR) (CO) ] (m/z 803), and after 1 week mainly the
2 2 6
bis-thiolate species, even in the presence of an excess of thiol,
Table 1. It is also worth noting that in some experiments there
was some of the mono-exchanged Re3 species present viz.
Ϫ
[
Re (OH) (SR)(CO) ] at m/z 985. This is in contrast to the lack
3
3
9
of a methoxy analogue observed when complex 1 is treated with
Fig. 1 Negative ion ES spectra (cone voltage 5 V) of a mixture of
Ϫ
Ϫ
methanol, giving [Re (µ-OMe) (CO) ] and unchanged [Re3-
[Re (µ-OH) (CO) ] 1 and n-dodecanethiol (RSH) in MeCN: (a) 25 min
2
3
6
2
3
6
Ϫ
(
OH) (CO) ] . One possibility is that the SR for OH exchange
has occurred on [Re (OH) (CO) ] directly, reflecting the
after addition, (b) after standing overnight, (c) after 1 week.
4
9
Ϫ
3
4
9
greater ability for (more acidic) thiols to protonate the less basic
strate the power of ESMS in monitoring reactions of such
thiols, which would be expected to give complex NMR spectra.
Ϫ
{
compared to [Re (OH) (CO) ] } OH groups of [Re (OH) -
2 3 6 3 4
Ϫ
(
CO) ] .
With 2-sulfanylethanol a (low intensity) intermediate ion at m/z
9
Ϫ
When p-toluenethiol is added to the methoxy complex
633 was observed, which may be [Re
2
(OH)(SCH
CH
2 2 6
CH O)(CO) ]
Ϫ
[
Re (µ-OMe) (CO) ] 2, exchange of OMe for SR groups
(containing a chelate ring Re–S–CH
2
2
–O) or less likely,
2
3
6
Ϫ
occurs, but slower than for the reaction of 1. This is presumably
due to the steric protection afforded by the methoxy groups.
After 20 min little reaction had occurred, while after standing
overnight there is fairly clean formation of the monosubstituted
[Re
(O)(SCH CH OH)(CO) ] .
2 2 2 6
On standing the solutions of complex 1 and the above thiols
Ϫ
overnight the tris(thiolate) anions [Re
formed in all cases (exclusively for 2-sulfanylethanol) but with
(SR)
(CO)
]
were
2
3
6
Ϫ
Ϫ
derivative [Re (OMe) (SR)(CO) ] , and after 1 week fairly clean
the bis-substituted species [Re
2
(OH)(SC12
H
25
)
2
(CO)
6
]
(m/z
2
2
6
formation of the bis-substituted compound, together with some
mono- and some tris-substituted species.
With benzeneselenol (PhSeH) and complex 1 similar results
959) the major species for 1-dodecanethiol. After 1 week,
Ϫ
almost exclusively [Re
(SC12
H
)
(CO)
]
6
(m/z 1144) and
2
25
3
Ϫ
[Re (SR) (CO) ]
(m/z 1631) (R = thioglucose tetraacetate)
2 3 6
were also obtained, with formation of the mono- and di-
were formed, indicating relatively slow reactions. ES spectra at
a cone voltage of 5 V showing the course of the reaction with
Ϫ
substituted species [Re (OH) (SePh) (CO) ] (n = 1 or 2)
2
3 Ϫ n
n
6
occurring rapidly, but with no evidence of formation of the
tris(selenolate) complex.
Similar results were obtained with mixtures of complex 1 and
dodecanethiol are given in Fig. 1. Addition of an excess of
Ϫ
water to the solutions of [Re
(SC12
H
)
3
(CO)
] or [Re
(SCH
2
-
2
2
25
6
Ϫ
CH OH) (CO) ] caused no reversal to hydroxy species even
2 3 6
n-dodecanethiol, n-C H SH, β--thioglucose tetraacetate 3,
after standing for 1 week, demonstrating the stability of the
Re–thiolate combination. This could be due to stronger Re–S
than Re–O bonds, and the fact that water is a weaker acid
12
25
(
pK ca. 16) compared to thiols (pK ca. 10).
a
a
Ϫ
Thiolate-bridged species of the type [Re (µ-SR) (CO) ] have
2
3
6
been described previously, for example the tris(thiobenzoate)
Ϫ
complex [Re {SC(O)Ph} (CO) ] , which was prepared from
2
3
6
[
ReBr(CO) ] and PhC(O)SM (M = K or Cs), has been shown
5
by an X-ray crystallographic study to contain three bridging
5
or 2-sulfanylethanol (HSCH CH OH) except that the rate of
SR groups. The complexes [Et N] [M (µ-SCH CH OH) (CO) ]
2
2
4
2
2
2
2
3
6
reaction appeared somewhat slower with the bulky thiols,
possibly due to their greater steric bulk. These studies demon-
(M = Tc or Re) were prepared by reaction of [Et N] -
4 2
[MCl (CO) ] with 2-sulfanylethanol, and the technetium
3
3
J. Chem. Soc., Dalton Trans., 2000, 3204–3211
3205

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6
complex was structurally characterised. A series of complexes
t
[
Et N][Re (µ-SR) (CO) ] (R = Me, Bu , Ph or C F ) were pre-
4
2
3
6
6
5
n
pared by reaction of [Et N][Re (µ-Br) (CO) ] with [SnBu -
4
2
3
6
3
7
(
SR)] in refluxing methanol. Other methods, employing the
sodium salt of the thiolate and a variety of other rhenium pre-
Ϫ
Ϫ
2Ϫ
cursors [Re Br (CO) ] , [ReBr (CO) ] , [ReBr (CO) ] , have
2
3
6
2
4
3
3
7,8
also been described for the synthesis of this type of complex.
Finally, reactions of [MCp (SPh) ] (M = Mo or W) with
2
2
5
[
Re (CO) ] give complexes containing the fulvalene (µ-η :
2 10
5 9
η -C H ; Fv) ligand, [M FvCp (µ-SPh)][Re (µ-SPh) (CO) ].
10
8
2
2
2
3
6
These complexes form part of a general class of the type [Re -
2
Ϫ
10
(
µ-X) (CO) ] , e.g. where X = anionic ligand. Thiolate ligands
3 6
are well known for their ability to bridge metal centres, but
relatively few thiolate-containing dinuclear complexes contain-
11
ing three thiolate bridges have been synthesized, though there
are a number of examples of complexes [(OC) M(µ-SR) -
4
2
1
2
M(CO) ] (M = Mn or Re) and of other rhenium carbonyl
complexes containing bridging thiolate ligands. Relatively few
examples appear to exist regarding the synthesis of thiolate
4
13
14,15
complexes from alkoxide complexes,
however, the ESMS
studies described in this paper strongly suggest that it could be a
very successful and convenient approach.
When the cone voltage is increased to 50 V the mono-
p-toluenethiolato species (in a solution containing mainly this
Ϫ
species) undergoes dehydration to give [Re (O)(SR)(CO) ] at
2
6
Ϫ
m/z 679 and [Re (O)(SR)(CO) ] at m/z 651. In contrast, the
2
5
bis-thiolate species is stable at 50 V, with no fragmentation
occurring. The monosubstituted species [Re (OH) (SePh)-
2
2
Ϫ
(
(
CO)6]Ϫ also undergoes dehydration giving [Re (O)(SePh)-
CO)6] at m/z 712. The dehydration of the mono-thiolate
2
derivatives is the same behaviour as that observed for
monosubstituted alkoxy and phenoxy derivatives, discussed
in the preceding paper. On applying a cone voltage of 30 V to
Ϫ
Fig. 2 Negative ion ES spectra of [Re (µ-SH) (CO) ] (generated from
2
3
6
Ϫ
[
Re (µ-OH) (CO) ] 1 and H S) in MeCN solution at cone voltages of
a) 5 and (b) 50 V, showing fragmentation by loss of H S and CO.
2
2 3 6 2
(
Ϫ
the monosubstituted ion [Re (OH) (SCH CH OH)(CO) ] the
2
2
2
2
6
Ϫ
species [Re (O)(SCH CH OH)(CO) ] (m/z 633) was formed.
2
2
2
6
Ϫ
solution had turned pale yellow, and [Re (µ-SH) (CO) ] was
the dominant ion, with a small amount of 1, and traces of
mono- and di-substituted species. No (OH → SH) exchange
was observed on the trinuclear species [Re (OH) (CO) ] . On
2
3
6
At elevated cone voltages (50–70 V) the bis- and tris-substituted
Ϫ
Ϫ
ions [Re (OH)(SC H ) (CO) ] and [Re (SC H ) (CO) ] are
2
12 25
2
6
2
12 25
3
6
stable towards fragmentation by dehydration, as is also found
for the bis(p-toluenethiolate) species above. This is consistent
with two or more OH groups being required for intramolecular
facile dehydration reaction to proceed, as would of course be
expected. No evidence of fragmentation by β-hydride elimin-
Ϫ
3
4
9
increasing the cone voltage to 50 V the analogous fragmen-
Ϫ
1
tation pathway is observed for [Re (µ-SH) (CO) ] as for 1, i.e.
2
3
6
facile elimination of H S, together with CO loss, resulting in
2
Ϫ
Ϫ
Ϫ
the ions [Re
(m/z 577), and [Re
2
(S)(SH)(CO)
(S)(SH)(CO) ]
4
]
6
(m/z 605), [Re
(S)(SH)(CO)
2
]
5
ation was observed for [Re (SC H ) (CO) ] at 70 V. Similarly,
2
Ϫ
12 25
3
6
Ϫ
(m/z 549). Spectra at
2
[
Re (SCH CH OH) (CO) ] showed appreciable stability at 50
2 2 2 3 6
cone voltages of 5 and 50 V are shown in Fig. 2. At 70 V the
V, with a base peak of the parent ion, and low intensity ions at
Ϫ
dominant ions observed are [Re (S)(SH)(CO) ] (m/z 521) and
2
3
m/z 665 and 693 ascribed to [Re (SCH CH O)(SCH CH OH)-
2
2
2
2
2
Ϫ
Ϫ
[Re
(S)(SH)(CO) ] . After standing for several days, the 5 V
2 4
Ϫ
(
CO)n] (n = 5 and 6), formed by elimination of 2-sulfanyl-
spectrum of [Re (µ-SH) (CO) ] also showed (unassigned)
2
3
6
ethanol. In contrast, the methoxy and ethoxy derivatives
Ϫ
species at m/z 454 and 1276.
The species [Re (µ-SH) (CO) ] appears to be stable towards
6
water, since a solution in MeCN still showed the ion as the
base peak after addition of an excess of water and standing for
days. However, the addition of NaOH results in rapid
reconversion into [Re (µ-OH) (CO) ] , together with some
ReO4 (m/z 251). When smaller quantities of NaOH are used
the intermediate mixed OH/SH species [Re (µ-OH) (µ-SH)3 Ϫ n-
CO) ] (n = 1 or 2) can be observed. It is noteworthy that the
6
Ϫ
species [Re (SH) (CO) ] has not been reported, perhaps due to
[
Re (OR) (CO) ] undergo facile β-hydride elimination pro-
2 3 6
1
Ϫ
2
3
cesses at cone voltages of 50 V and higher. Presumably, the
stability of the C᎐O bond (compared to a C᎐S bond) formed on
᎐
᎐
β-hydride elimination is the major driving force for the reaction
with alkoxides when compared to thiolates; the stability of a
Re–S compared to a Re–O bond may also be a contributing
factor.
3
Ϫ
2
3
6
Ϫ
2
n
Ϫ
(
Reactions of complex 1 with H S and Na S
2
2
2 3 6
lack of a convenient synthetic route.
No reaction was observed between complex 1 and Na S in
2
MeCN–water solution, consistent with the requirement for
Reactions of complex 1 with difunctional thiolate ligands
‘
acidic’ protons to be present in the incoming ligand. Na S will
2
2Ϫ
Ϫ
Ϫ
act as a source of base (S ϩ H O → SH ϩ OH ), and
consistent with this the intensity of the [Re (OH) (CO) ] ion
Thiosalicylic acid. Selected data for the thiosalicylate system
2
Ϫ
are summarised in Table 1. Thiosalicylic acid (H tsal, 4) is able
3
4
9
2
(
m/z 878) decreased markedly on addition of Na S, similar to
to co-ordinate to metal centres as either a monoanion or
dianion, and can show a variety of bonding modes, from
2
Ϫ
1
the addition of OH , as described previously.
16,17
In contrast, H S (a weak acid) reacted with complex 1 in
monodentate, to chelating, and bridging.
The 5 V ESMS
2
MeCN quite quickly, giving initially a mixture of 1, mono-, di-
spectrum of complex 1, to which a small quantity of thio-
salicylic acid had been added, showed complete and rapid
(several minutes) consumption of 1 and formation of two new
Ϫ
and tri-substituted species [Re (µ-OH) (µ-SH)3 Ϫ n(CO)6] at
2
n
m/z 591, 607, 623 and 639 respectively, at a cone voltage of 5 V.
Data are summarised in Table 1. After standing overnight, the
species, the mono(thiosalicylate)-substituted ion [Re (OH)-
2
3
206
J. Chem. Soc., Dalton Trans., 2000, 3204–3211

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Ϫ
Ϫ
(
tsal)(CO)6] at m/z 709 and [Re (OH) (Htsal)(CO) ] (m/z
2 2 6
7
27). A possible structure for this ion is 5, with a bridging
I
thiolate ligand (if it is assumed that Re is soft in character),
though an isomer with a bridging carboxylate is also possible. A
likely structure for the m/z 709 species would contain one OH
bridge, a bridging thiolate, together with a bridging oxygen
from the carboxylate, i.e. 6. This would maintain the expected
six-co-ordination at both rhenium centres, while minimising
steric strain; a structure involving bridging by both carboxylate
oxygens, Re–O–C–O–Re, would probably be too strained. The
acetonitrile solvated analogue of 6, [Re (OH)(tsal)(CO) -
2
6
Fig. 3 Negative ion ES spectrum (cone voltage 5 V) of [Re (µ-OH) -
2
3
Ϫ
(
1
CO)6] 1 and benzene-1,4-dimethanethiol, HSCH C H CH SH, after
2 6 4 2
week reaction in MeCN. The inset shows a comparison of (a) experi-
mental and (b) calculated isotope distribution patterns for the aggregate
dianion 8 at m/z 811.
3
-Sulfanylpropionic acid, HSCH CH CO H. When a small
2 2 2
quantity of 3-sulfanylpropionic acid is added to complex 1 and
the ES spectrum recorded at 5 V a new peak due to the mono-
Ϫ
Ϫ
(
MeCN)] (m/z 750), was also observed at 5 V. This species is
substituted species [Re
2
(OH)
2
(SCH
2
CH CO
2
2
H)(CO)
]
6
(m/z
likely still to contain the thiolate bridge and a co-ordinated
MeCN, perhaps with a monodentate (non-bridging) carboxyl-
ate group.
Upon allowing the solution to stand for ca. 25 min new
mononuclear ions identified as [Re(tsal)(CO) ] (m/z 423) and
Re(tsal)(CO) (NH )] (m/z 440) are observed, while [Re2-
OH) (Htsal)(CO) ] (m/z 727) had almost disappeared, with
Re (OH)(tsal)(CO) ] (m/z 709) the base peak. The source of
679) is seen. When an excess of the acid is added to 1 the latter
was consumed and new intense ions at m/z 790 and 855 were
observed, assigned as [Re
(SCH
(SCH
tively. Increasing the cone voltage to 30 V results in loss of
MeCN from the former ion, giving [Re (SCH CH CO )-
at m/z 749. The ion [Re (SCH CH
] was not observed for thiosalicylic acid, possibly
CH
CO
)(SCH
CH
CO
respec-
H)-
2
2
2
2
2
2
2
Ϫ
Ϫ
(MeCN)(CO)
]
6
and [Re
CH
CO
H) (CO)
]
6
2
2
2
2
3
Ϫ
3
Ϫ
[
(
[
2
2
2
2
3
3
Ϫ
Ϫ
(SCH
CH
CO
H)(CO)
]
6
-
2
2
6
2
2
2
Ϫ
2
2
Ϫ
CO H)
(CO)
3
2
6
2
6
the ammonia is adventitious ammonia present in the aceto-
nitrile solvent used. No di- or tri-thiosalicylate substituted
species were observed, consistent with thiosalicylate being a
good chelating and bridging ligand, able to take up two
co-ordination sites on the Re.
because the backbone of the thiosalicylate ligand is rigid, with
the SH and CO H groups ortho to each other, promoting chel-
ation, and making the formation of a tris-substituted product
2
unfavourable on steric grounds. On standing overnight (and
Ϫ
after 1 week) the [Re
(SCH
CH CO
2
H)
2
(CO) ]
6
ion was the
2
2
3
On standing overnight only 2 ions are observed in the 5 V
dominant Re-containing ion, together with a minor ion at
Ϫ
Ϫ
spectrum, [Re(tsal)(CO) ] (m/z 423, the base peak) and some
m/z 1231, assigned as [Re
higher cone voltage of 50 V the Re
intensity, and [Re (SCH CH CO H)
undergo fragmentation to give [Re (SCH
at m/z 749, by loss of HSCH
3
(SCH
2
CH
2
CO
2 4 9
H) (CO) ] . At the
3
Ϫ
[
2
Re(tsal)(CO) (NH )] (m/z 440). At the higher cone voltage of
3
ion remained at low
3
3
Ϫ
Ϫ
0 V the [Re(tsal)(CO) ] ion becomes the base peak, indicating
2
2
2
2
(CO)
3
6
]
appeared to
CO )(SCH CH
H)(CO) CH CO H.
(SCH CH is analogous to [Re (SCH
OH) (CO) ] reported previously. These ESMS observ-
6
3
facile loss of the weakly co-ordinated NH ligand. Additionally
2
CH
2
2
2
2
-
2
3
Ϫ
at 20 V decarboxylation of the thiosalicylate ligand begins to
CO
[Re
CH
2
]
6
2
2
2
Ϫ
Ϫ
occur, giving the ion [Re(SC H )(CO) ] at m/z 379. Decarb-
2
2
2
CO
2
H) (CO)
3
]
6
2
-
2
6
4
3
Ϫ
6
oxylation of thiosalicylate ligands in ESMS spectra of
2
3
17
18
platinum(), mercury() and gold() complexes has been
observed previously. A new species at m/z 1115 also appears in
ations are consistent with the thiolate ligand derived from
3-sulfanylpropionic acid being more flexible than that derived
from thiosalicylic acid, the latter preferring to form chelate
complexes. It is also noteworthy that, compared to carboxylic
the 30 V spectrum (and in spectra at higher cone voltages up to
Ϫ
7
[
0 V), tentatively assigned as [Re (tsal) (CO) ] . By 50 V the ion
3
2
9
Ϫ
Re(SC H )(CO) ] (m/z 351) dominates the spectrum, together
with [Re(SC H )(CO) ] (m/z 379) and [Re(SC H )(CO)] (m/z
23). At 70 V the ions [Re(SC H )] (m/z 295) and [Re(SC H )-
6 4 6 4
Ϫ
CO)] (m/z 323) dominate. After standing the rhenium–
thiosalicylate solution for 2 weeks the [Re(tsal)(CO)3] ion at
m/z 423 was essentially the only species observed at 5 V. It is
worth noting that the dimeric manganese analogue of this ion,
Mn (tsal) (CO) ] , has been characterised by an X-ray diffrac-
tion study. Rhenium thiosalicylate complexes have been syn-
acids (which cleave the Re dimer forming monorhenium
2
1
6
4
2
Ϫ
Ϫ
carboxylate species), no such species were observed with 3-
sulfanylpropionic acid, presumably because of the formation
of three strong Re–S–Re bridges which stabilise the complex.
6
4
3
6
4
Ϫ
3
(
Ϫ
Benzene-1,2- and -1,4-dimethanethiol, HSCH
These dithiols were investigated to see if the Re
C
H
CH
6
SH.
2
2
6
4
(CO) units
2
2Ϫ
[
could be linked together. Addition of benzene-1,4-dimethane-
2
2
1
6
9
thiol to complex 1 in MeCN gave the usual species in the ESMS
Ϫ
Ϫ
thesized by reaction of [ReCl(CO) ] with thiosalicylic acid,
spectrum at 5 V: [Re
2
(µ-OH)
3
(CO) ]
6
and [Re
3
(OH)
(OH)
] 7 at m/z 743, which increased in intensity
with time. On standing overnight, the monosubstituted species
was the base peak, with some disubstituted [Re (OH)(SCH
C H CH SH) (CO) ] (m/z 895). On standing for 1 week the
6 4 2 2 6
4
(CO)
9
] ,
5
giving a neutral dimeric complex [Re (HSC H CO ) (CO) ]
together with the mono-thiolate complex [Re
2
2
(SCH
-
2
2
6
4
2
2
6
Ϫ
with bridging carboxylates, and an equilibrium mixture of the
C H CH SH)(CO)
6 4 2 6
tautomeric monomer species [Re{OC(O)C H SH}(CO) L] and
6
4
3
20
[
Re{SC H C(OH)O}(CO) L] (L = thf or Et O). The anionic
species [Re(SC H CO )(CO) (thf)] , closely related to one
2
-
2
6
4
3
2
Ϫ
Ϫ
6
4
2
3
of the ions observed in this electrospray study, was also
disubstituted species dominated the spectrum, together with a
new species at m/z 811, Fig. 3. Examination of the isotope
ϩ
synthesized as its AsPh4 salt.
J. Chem. Soc., Dalton Trans., 2000, 3204–3211
3207

View Article Online
pattern indicated that this species was a dianion, with the
Reactions of complex 1 with dithiocarbamates
Addition of a small quantity of NH [S CN(CH ) ] to complex
characteristic 0.5 m/z separation of peaks. The species [{Re -
2
2
Ϫ
4
2
2 4
(
OH)(SCH C H CH SH)(CO) } (SCH C H CH S)] gives a
2 6 4 2 6 2 2 6 4 2
1
before running the negative-ion ESMS spectrum gave {in
good match to the observed isotope pattern, Fig. 3 inset. A
reasonable structure, based on the chemistry of this system, is 8,
with two Re (µ-OH)(CO) groups bridged by a [SCH C H -
Ϫ
addition to unchanged 1 and [Re (OH) (CO) ] }, ions assigned
3
4
9
as the mono- and di-substituted species [Re (OH) {S CN-
2
2
2
2
6
2
6
4
Ϫ
Ϫ
(
CH ) }(CO) ] and [Re (OH){S CN(CH ) } (CO) ] at m/z
2Ϫ
2 4 6 2 2 2 4 2 6
CH S] ligand, and each S atom bridging a different Re unit.
2
2
7
20 and 849 respectively. The tris(dithiocarbamate) ion
Ϫ
The observation of this species again demonstrates the utility
of the electrospray technique, and suggests that complex aggre-
[
Re {S CN(CH ) } (CO) ] was not observed. On standing, the
2 2 2 4 3 6
Ϫ
intensity of [Re (OH){S CN(CH ) } (CO) ] increased after
2
2
2
4
2
6
gates built from polyfunctional ligands and Re (CO)6 units
2
several minutes. After standing overnight (there was no sig-
nificant further change after 1 week) the major ion is a new
should be possible.
For benzene-1,2-dimethanethiol the mono-substituted ion
species at m/z 563, assigned to the monorhenium species
Ϫ
[
Re (OH) (SCH C H CH SH)(CO) ] (m/z 743) was formed
2
2
2
6
4
2
6
Ϫ
[
Re{S CN(CH ) } (CO) ] . The dithiocarbamate ligand is
2
2
4
2
3
quickly as the sole ion in the 5 V spectrum, in addition to
unchanged complex 1. On standing overnight all the m/z 743
ion disappeared, and was replaced by an ion at m/z 725 (plus an
unidentified weak ion at m/z 895), formed by loss of water from
the m/z 743 ion. At this low cone voltage no dehydration is
expected to occur as a result of the ES process, and so this
ion can tentatively be assigned to the species 9, containing a
capable of acting in either the chelating or (less commonly)
21
bridging mode, and the conversion of the dirhenium species
Ϫ
into [Re{S CN(CH ) } (CO) ] is not completely unexpected.
2
2
4
2
3
Two weak ions, at m/z 1021 and 1049, were also observed; the
Ϫ
former is assigned as [Re {S CN(CH ) } (MeCN)(CO )] .
2
2
2
4
3
6
The reaction of complex 1 with Na(S CNEt ) in MeCN–
2
2
water (to aid solubility) proceeded very slowly, but gave similar
ions. After standing overnight, small ions at m/z 567 and 853
Ϫ
assigned as [Re(S CNEt ) (CO) ] and [Re (OH)(S CNEt ) -
2
2
2
3
2
2
2 2
Ϫ
Ϫ
(
CO)6] respectively were observed, together with S CNEt
2 2
Ϫ
and Na(S CNEt ) . No mono-substituted species was
2
2 2
Ϫ
observed in this case. After 1 week, [Re(S CNEt ) (CO) ] was
the major species observed, with [Re (OH)(S CNEt ) (CO) ]
2
2
2
3
Ϫ
2
2
2
2
6
at ca. 30% relative intensity. Rhenium carbonyl dithiocarb-
amate species are known, for example from reaction of tetra-
ethylthiuram disulfide, (Et NCS ) , with [ReCl(CO) ], giving
2
2
2
5
species such as [Re(S CNEt ) (CO)], [Re(S CNEt )(CO) ] and
2
2
3
2
2
3 2
Ϫ 22
[
ReCl(S CNEt )(CO) ] . The difference in reactivity of the
2 2 3
two dithiocarbamates studied may be related to the fact that
one was an ammonium salt (which contains relatively acidic
protons, promoting the reaction of 1), while the less reactive
was a sodium salt.
bridging OH group, and a benzenedimethanethiolate ligand
with thiolate bridges to both rhenium centres. The 1,4 isomer is
unable to co-ordinate in this manner, accounting for the differ-
ence between the two thiols. After standing the solution for 1
week the 5 V ES spectrum still shows the m/z 725 ion as the base
peak, together with an ion at m/z 877, assigned as the analogue
in which the OH group has been replaced by a mono-
deprotonated thiol, i.e. 10. Thus, ESMS can conveniently be
used to explore the co-ordination chemistry of related ligands.
Reactions of complex 1 with thiocyanate, selenocyanate, and
thiosulfate ions
Addition of an excess of KSCN to complex 1 resulted in
initial formation of some of the monosubstituted species
Ϫ
[Re (OH) (SCN)(CO) ] (m/z 632) observed at a cone voltage
2
2
6
of 5 V, and after ca. 20 min the di- and tri-substituted species
3
208
J. Chem. Soc., Dalton Trans., 2000, 3204–3211

View Article Online
Ϫ
Ϫ
Ϫ
[
(
Re (OH)(SCN) (CO) ] (m/z 673) and [Re (SCN) (CO) ]
Table 2 ESMS data for reactions of [Re
2
(µ-OH)
3
(CO)
6
]
1 with
2
2
6
2
3
6
nitrogen ligands, after reaction for 1 week in MeCN solution; cone
m/z 714) were also seen, in addition to solvated species all
Ϫ
Ϫ
voltage 5 V
containing three SCN ligands: [Re (SCN) (MeCN)(CO) ]
2
Ϫ
3
6
(
(
m/z 755), [Re (SCN) (MeCN) (CO) ] (m/z 796), and [Re2-
2 3 2 6
Ϫ
SCN) (MeCN) (CO) ] (m/z 837). The observation of the
a
Ligand
Major product ions (m/z, %)
3
3
6
solvated ions possibly suggests non-bridging behaviour of some
SCN ligands, leaving vacant co-ordination sites which are
Ϫ
Ϫ
PhNH
p-O NC H NH
2
[Re
2
(µ-OH)
2
(NHPh)(CO)
6
]
(666, 30%)
Ϫ
[Re (µ-OH) (NHC H NO )(CO) ] (711, 10%)
2
6
4
2
2
2
6
4
2
6
filled by MeCN solvent molecules, though the structures of
these ions are unknown. In this regard it is noteworthy that
solvated adducts of other tris-substituted species [Re (µ-X) -
Ϫ
p-MeOC H NH
[Re (µ-OH) (NHC H OMe)(CO) ] (696, 3%)
2 2 6 4 6
Ϫ
6
4
2
MeC(O)NH2
PhC(O)NH2
[Re (µ-OH) {NHC(O)Me}(CO) ] (632, 100%)
2 2 6
Ϫ
2
3
[Re (µ-OH) {NHC(O)Ph}(CO) ] (694, 100%)
2
2
6
Ϫ
(
CO) ] are not seen, with the exception of weak aqua adducts
of [Re (µ-OH) (CO) ] . After standing for 2 days, mono-
a
6
Identified by the most intense peak in the isotope distribution pattern,
Ϫ 1
2
3
6
calculated using the ISOTOPE program.
rhenium species were the dominant ions in the 5 V spectrum,
Ϫ
namely [Re(SCN) (CO) ] (m/z 387) and its solvated analogues
2
3
Ϫ
Ϫ
and exchange reactions of the platinum() hydroxo dimer
[
(
Re(SCN) (CO) (H O)] (m/z 405), [Re(SCN) (MeCN)(CO) ]
2 3 2 2 3
Ϫ
2ϩ
[(Ph
P)
Pt(µ-OH)
Pt(PPh
)
]
with amines and hydrazine have
P) Pt(µ-OH)-
Pt(PPh
3
2
2
3
2
m/z 428) and [Re(SCN) (MeCN) (CO) ] (m/z 469), in add-
2 2 3
Ϫ
also recently been reported to give the species [(Ph
3
2
ition to some unchanged 1, [Re (OH) (CO) ] , and [Re -
3
4
9
2
2ϩ
2ϩ 26
Ϫ
(µ-NHR)Pt(PPh
3
)
2
]
and [(Ph
3
P)
2
Pt(µ-NHR)
2
) ] .
3 2
(
SCN) (MeCN) (CO) ] (n = 2 or 3), again consistent with the
3
n
6
ESMS data for the various species observed in this study are
summarised in Table 2.
The reaction of complex 1 with an excess of aniline in MeCN
proceeded slowly, but after 1 week, about 30% of the starting
had converted into [Re (µ-OH) (NHPh)(CO) ] (m/z 666),
which presumably contains a bridging amido group, Re–
NHPh–Re, 11. Analogous weak ions were observed with
relatively poor bridging ligand abilities of thiocyanate ions in
the Re system. Addition of KSeCN to 1 also gives the mono-
2
Ϫ
substituted species [Re (OH) (SeCN)(CO) ] at m/z 680 in the
2
2
6
5
V ESMS spectrum. No disubstituted species was observed,
Ϫ
1
2
2
6
even though an excess of selenocyanate was available for
Ϫ
reaction, as shown by the presence of an intense SeCN ion
at m/z 106.
Addition of sodium thiosulfate to complex 1 in MeCN–
water solution resulted in no immediate reaction, but after
2
days most of the original 1 had been consumed, the major
Ϫ
species observed in the 5 V spectrum being [Re(S O )(CO) ]
2
3
3
Ϫ
(
m/z 383) and [Re(S O )(CO) (H O)] (m/z 401), with a small
2 3 3 2
Ϫ
amount of [Re (OH)(S O )(CO) ] at m/z 669.
2
2
3
6
Attempted reaction of complex 1 with a primary phosphine
One of us recently reported the synthesis of the completely
23
air-stable primary phosphine RCH PH (R = ferrocenyl); pre-
2
2
p-nitroaniline and p-methoxyaniline. The reaction is much
slower than that with most alcohols, phenol, and thiols,
probably due to the much lower acidity of NH compared to
that of OH and SH protons. It is also worth noting that the
liminary studies suggest that the reactivity of this phosphine
towards metal centres is not curtailed by its air-stability. Given
the similarity in the chemistries of thiols and primary phos-
phines, we wished to investigate the synthesis of phosphido-
bridged dirhenium complexes, monitoring reactions using
ESMS. Rhenium carbonyl complexes with bridging phosphido
ligands have been prepared previously, e.g. [Re (µ -H) -
Ϫ
intensity of the m/z 878 ion, [Re (OH) (CO) ] , typically
3
4
9
observed in spectra of 1, was of markedly lower intensity
with added basic amines; the addition of hydroxide causes the
3
3
2
1
same effect, as noted in the preceding paper. In contrast, the
24
(
µ-PPh ) (CO) ] and [Re(µ-PPh )(CO) ] , though we are not
2 3 6 2 4 2
Ϫ
reactions of 1 with a selection of primary alkylamines (MeNH ,
2
aware of any analogues of the type [Re (µ-PR ) (CO) ] .
2
2
3
6
n
EtNH , Bu NH , PhCH NH ) resulted in large numbers of
2
2
2
2
The addition of an excess of RCH PH to complex 1, followed
2
2
unidentified ions together with residual complex 1 after stand-
ing for 1 week.
We therefore turned our attention to amides, RC(O)NHRЈ,
where the NH proton is much more acidic than in a free amine.
by recording the ESMS spectrum, surprisingly did not yield any
such complexes after 1 hour, indicating a slower reaction than
between 1 and thiols. After standing at room temperature for
1
week, 1 dominated the spectrum, together with some [Re -
3
Ϫ Ϫ
Typical pK values for amine and amide protons are 40 and 15
a
(
OH) (CO) ] , a trace of ReO , and a small new ion at m/z
4
9
4
respectively; the latter compares favourably with the value of
Ϫ
8
37, which could be [Re (OH) {PH(S)CH R}(CO) ] (from
2 2 2 6
alcohols (pK ca. 16). No reaction was observed between com-
a
adventitious S8 in the mass spectrometer) or [Re (OH) -
2
2
plex 1 and either acetanilide [CH C(O)NHPh] or N-phenyl-
Ϫ
Ϫ
3
{
PH(O) CH R}(CO) ] , possibly formed by ReO catalysed
2
2
6
4
benzamide [PhC(O)NHPh], presumably because of the steric
bulk of the amide ligand. However, with the primary amide
acetamide, MeC(O)NH , the monosubstituted species [Re -
oxidation (since RCH PH is completely air-stable in solution
2
2
on its own). Simpson and Bergman have commented upon the
2
2
very slow reaction of the mononuclear complex [Re(OEt)-
Ϫ
(
µ-OH) {NHC(O)Me}(CO) ] (m/z 632) was formed slowly but
2
2
6
(
CO) (Et PCH CH PEt )] with Ph PH, observations which are
3
2
2
2
2
2
cleanly. After standing overnight the monosubstituted ion was
the base peak, and there was a trace amount of the bis-
substituted species, but no tris-substituted species, as shown in
Fig. 4. After 1 week only a small amount of 1 remained, and the
paralleled here.
Reactions of complex 1 with nitrogen donor ligands (amines and
amides)
Ϫ
dominant ion was [Re (µ-OH) {NHC(O)Me}(CO) ] , suggest-
2
2
6
As a result of the facile exchange reactions which occur
between complex 1 and alcohols or thiols we were interested
in exploring the possibility of exchange reactions with amines
and amides. The mononuclear alkoxide complexes [Re(OR)-
ing it is a good target for subsequent synthetic studies on
a macroscopic scale. Benzamide, PhC(O)NH , behaved very
2
Ϫ
similarly, giving the ion [Re (µ-OH) {NHC(O)Ph}(CO) ]
2
2
6
(m/z 694) except that there was no trace of the bis-substituted
product. Clearly, the NH protons of primary amides are much
more reactive than those of secondary amides. Mononuclear
(
CO) L ] (R = Me or Et; L = bidentate phosphine or
3
2
2
arsine) react reversibly with aniline to give the amido complex
2
2
[
Re(NHPh)(CO) L ]. Amido ligands are able to act as mono-
rhenium() amide derivatives of the type trans-[Re{η -
3
2
25
27
dentate or bridging ligands towards transition metal centres
NHC(O)Ph}(CO) (PPh ) ] have been synthesized. In contrast
2
3 2
J. Chem. Soc., Dalton Trans., 2000, 3204–3211
3209

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1
,2-dimethanethiol (Aldrich), benzene-1,4-dimethanethiol
(
(
(
Aldrich), benzeneselenol (Aldrich), adenine (Aldrich), thymine
Aldrich), acetamide (BDH), aniline (BDH), p-nitroaniline
BDH), benzamide (BDH), acetanilide (BDH), sodium
diethyldithiocarbamate (BDH), ammonium tetramethylene-
dithiocarbamate (BDH), potassium thiocyanate (BDH), potas-
sium selenocyanate (BDH), and sodium thiosulfate (BDH).
Electrospray mass spectrometry
Details of the instrumentation and conditions used are given in
1
the preceding paper. All major ions were identified by com-
32
parison of their observed and calculated isotope distribution
patterns.
Acknowledgements
We thank the National University of Singapore (RP 950695),
the National Institute of Education, Singapore (RP 15/95
YYK), the University of Waikato, and the New Zealand
Lottery Grants Board for financial support. W. H. thanks the
Asia 2000 Foundation of New Zealand for a travel grant, and
Wendy Jackson for technical assistance.
Fig. 4 Negative ion ES spectrum (cone voltage of 5 V) of [Re (µ-OH) -
2
3
Ϫ
(
CO)6] 1 and acetamide, after standing overnight in MeCN, showing
Ϫ
the formation of the amido species [Re (OH) {NHC(O)Me}(CO) ] at
2
2
6
m/z 632.
to the reactions with carboxamides, 1 did not react with an
excess of urea [H NC(O)NH ] in MeCN–water over a period of
References
2
2
1
week.
1 C. Jiang, T. S. A. Hor, Y. K. Yan, W. Henderson and L. J.
McCaffrey, J. Chem. Soc., Dalton Trans., 2000, 3197.
2
R. D. Simpson and R. G. Bergman, Organometallics, 1992, 11,
Reactions of complex 1 with the nucleosides adenine and thymine
3
980.
Complexes 1 and 2, and several other rhenium() alkoxo/
3 A. Egli, K. Hegetschweiler, R. Alberto, U. Abram, R. Schibli,
R. Hedinger, V. Gramlich, R. Kissner and P. A. Schubiger,
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hydroxo carbonyl complexes, were recently shown to have sig-
28
nificant anti-tumour activity in vitro. The complexes inhibit
DNA synthesis and also cause DNA fragmentation. We were
therefore interested in carrying out some preliminary studies
with DNA bases. Understanding the interactions of metal
centres with DNA components is of vital importance in the
development of metallodrugs, such as the archetypal cisplatin,
cis-[PtCl (NH ) ], a complex which interacts (after hydrolysis)
4
C. Jiang, Y.-S. Wen, L.-K. Liu, T. S. A. Hor and Y. K. Yan,
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39.
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3 2
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29
with the nitrogen atoms of guanine groups present in DNA.
A solution of complex 1 and adenine (HA, 12) dissolved in
9
M. J. Calhorda, M. A. A. F. de C. T. Carrondo, A. R. Dias, V. Félix,
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1
1
1
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1
2
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MeCN (with some Me SO to aid solubility) resulted in form-
2
Ϫ
5
404.
ation of the monosubstituted species [Re (OH) (A)(CO) ] (m/z
2
2
6
1
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08); this was the major ion after standing for 3 days, together
Ϫ
with some [Re (OH) (CO) ] (m/z 878). A corresponding ion
3
4
Ϫ
9
[
Re (OH) (T)(CO) ] (m/z 699) was observed for thymine (HT;
2 2 6
1
3). The imido proton of thymine is known to be quite acidic
30 31
(
pK 9.9); adenine has a similar pK of 9.8, probably for the
a
a
1
1
1
primary amino group. Further studies are in progress regarding
the interaction of 1 with important biomolecules.
Experimental
Materials
4
The compounds [Et N][Re (µ-OR) (CO) ] (R = H or Me) and
the phosphine RCH PH2 were synthesized by the literature
procedures. H S was prepared by addition of dilute HCl to
Na Sؒ9H O (BDH). The following compounds were obtained
4
2
3
3
6
2
2
2
2
2
from commercial sources and used as supplied: p-toluenethiol
(Aldrich), n-dodecanethiol (Aldrich), 2-sulfanylethanol
(Sigma), thiosalicylic acid (Sigma), 3-sulfanylpropionic acid
(Aldrich), β--thioglucose tetraacetate (Aldrich), benzene-
5
09, 259.
1
7 L. J. McCaffrey, W. Henderson, B. K. Nicholson, J. E. Mackay and
M. B. Dinger, J. Chem. Soc., Dalton Trans., 1997, 2577.
3
210
J. Chem. Soc., Dalton Trans., 2000, 3204–3211

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